1. Field of the Invention
This invention relates to a fuel control system for an engine.
2. Description of the Prior Art
There has been known a fuel control system for an engine in which the amount of fuel fed to the engine is temporarily increased during acceleration.
For example, in the fuel control system disclosed in Japanese Unexamined Patent Publication No. 1(1989)-219325, fuel is normally injected from an injector every predetermined crank angle for a predetermined time (synchronous injection), and is injected from the injector for a predetermined additional time (asynchronous injection) during acceleration.
That is, in the control system, the amount of fuel fed to the engine is increased in expectation of increase in the amount of intake air when the change in the throttle opening is large (when the vehicle is being accelerated) so that the air-fuel ratio does not become lean during acceleration. However, since the amount of fuel fed to the combustion chamber is the sum of fuel directly fed to the combustion chamber from the injector and fuel which has adhered to the wall of the intake manifold, evaporates and then flows into the combustion chamber, and since almost all the fuel which has adhered to the wall of the intake manifold is caused to flow into the combustion chamber at the beginning of the acceleration due to high intake vacuum downstream of the throttle valve which has been there before depression of the accelerator and remains there for a short time after the depression of the accelerator due to delay in change of the intake vacuum, the air-fuel ratio cannot become lean at the beginning of the acceleration but, during the acceleration thereafter, part of the fuel injected from the injector adheres to the wall of the intake manifold and the air-fuel ratio can become too lean, whereby acceleration performance deteriorates.